Rack, v. i. [imp. & p. p. Racked p. pr. & vb. n. Racking.]  To amble fast, causing a rocking or swaying motion of the body; to pace; -- said of a horse.
  Rack·ing, n. Naut. Spun yarn used in racking ropes.
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  racking
       adj : causing great physical or mental suffering; "a wrenching
             pain" [syn: wrenching]